I don't understand this statement.

UUIDs rarely have to be unique compared to every other place in the world where they are used, they just need to be unique within the same context. The reason for using NIC addresses and time is to ensure that the chance of a collision is really small (but not 0). Saying that you are making them a little more unique doesn't sound like good motivation.

The second part is that just using random numbers gives you no real guarantees of uniqueness since without seeding with time and NIC, it would be highly likely that multiple systems around the world would generate the same number.